Such a control device has been described in a connection with a piston and cylinder unit in the German utility model 7,502,826 (corresponding to U.S. Pat. No. 4,176,586). In this case the guide device took the form of a rail-like holding device, which was secured to the exterior of the cylinder. In the case of the sensors it was a question of reed switches and the piston able to move in the cylinder bore a magnet device able to operate the sensor without making contact therewith, when it moved into the range of response of the latter. In order to vary the time of actuation thereof, the sensors may be positioned on the guide device by displacement to any desired point within a working range.
An arrangement would also be conceivable in which the shifting adjustment of the respective sensor would involve detachment and re-attachment, in which case the guide device may be in the form of one or more simple holding devices.
For the transmission of the signal produced by the operation of a respective sensor prior sensors have been connected with signal conductors in the form of leads adapted to carry an electric current. If the sensors are not carefully handled or if a sensor should come into the path of motion of a moving workpiece, the lead may be torn off and the system will cease to be operational. The replacement of the sensors is an awkward operation since the connection lead has to be replaced as well and there is a danger of confusing the leads on re-assembly. A further relevant point is that the loosely placed leads present an untidy appearance, more especially if the pressure hose leading to the cylinders is loose as well.